In recent years, as their power and efficiency have increased and their cost decreased, LEDs have been used in many applications as viable replacements to conventional fluorescent lamps, incandescent lamps, neon tubes and fiber optic light sources. LED lighting systems can be employed in a variety of environments to illuminate a flat surface, such as street lighting, a parking lot, a parking garage, a roadway, a walkway, a sidewalk, an aisle, a hallway, a table, a stage, a room, a manufacturing facility, a warehouse, and other types of environments.
In applying these lights to these environments, a multitude of factors influences the choice of equipment, placement of fixtures, and degrees of illumination appropriate to the structures, terrain, and after-hours activity. Based on the LED lens selected for a particular application, hot spots of non-uniform light intensity, which are apparent to the eye human, can be created. A poor lighting design can create blinding spots of glare that cast shadows, creating an eyesore and a number of safety and security hazards. Thus, security ranks as a top concern for business owners having a commercial lighting system installed.
For example in a parking lot lighting system, visibility constitutes a major factor in every design. Parking lot lighting systems are actually regulated by the government, and by law must produce a minimum of four foot candles of light. Neglecting this element not only places drivers and pedestrians at risk in the parking lot, it can create for the business owner liability in the form of possible government fines and legal liability should an unfortunate incident occur on the premises due to poor visibility.
Thus, the optical specifications within the design of a lighting system typically identify application-specific radiation patterns required to be produced by the selected light source. For example, in some lighting applications, such as street lighting, parking garage lighting and walkway lighting, uniform illumination output from the light source is desired in order to uniformly illuminate the entire area.
However, this requirement may be difficult to attain when the target area has widely varying distances. To achieve uniform illumination over the entire area, it is necessary to tailor the intensity of the LED lens by increasing the intensity towards the more distant parts of the area, relative to the closest parts of the area.
For producing uniform illuminance on a flat surface, the ideal intensity distribution is given by an inverted cosine cube law (1/cos3 θ, variation where θ is the angle measured from the vertical direction of the lamp). Amplitude may change depending upon the power source, but the distribution shape still follows the inverted cosine cube law. An exact lens having the characteristics of “ideal” uniform illuminance cannot be produced.
Rather, some conventional techniques approach uniform illuminance without actually achieving “ideal” uniform illuminance. One such conventional technique is a batwing beam pattern, which is commonly used for illuminating a flat surface. The batwing pattern may be defined by having two roughly equal peaks in a candela distribution plot with a valley between the peaks at about 0 degrees. Some LED lamps that radiate the batwing intensity distribution can produce uniform illuminance, but none can produce an intensity distribution that follows the inverted cosine cube law.